Switches are typically electrically-controlled two-state devices that open and close contacts to effect operation of devices in an electrical or optical circuit. Relays, for example, typically function as switches that activate or de-activate portions of electrical, optical or other devices. Relays are commonly used in many applications including telecommunications, radio frequency (RF) communications, portable electronics, consumer and industrial electronics, aerospace, and other systems. More recently, optical switches (also referred to as “optical relays” or simply “relays” herein) have been used to switch optical signals (such as pulses of light traveling in fiber optics or other optical communication systems) from one path to another.
Although the earliest relays were mechanical or solid-state devices, recent developments in micro-electro-mechanical systems (MEMS) technologies and microelectronics manufacturing have made micro-electrostatic and micro-magnetic relays possible. Such micro-magnetic relays typically include an electromagnet that energizes an armature to make or break an electrical contact. When the magnet is de-energized, a spring or other mechanical force typically restores the armature to a quiescent position. Other electrostatic relays use voltage differences between a movable cantilever and a fixed electrode pad to generate electrostatic force that actuates an armature or cantilever. Other relays have used other actuation mechanisms, such as thermal actuation, shape memory alloy actuation, and the like. Such relays typically exhibit a number of marked disadvantages, however, in that they generally exhibit only a single stable output (i.e. the quiescent state) and they are not latching (i.e. they do not retain a constant output as power is removed from the relay). Moreover, the spring required by conventional micro-magnetic relays may degrade or break over time.
An example of a micro-magnetic relay is described in U.S. Pat. No. 5,847,631 issued to Taylor et al. on Dec. 8, 1998, the entirety of which is incorporated herein by reference. The relay disclosed in this reference includes a permanent magnet and an electromagnet for generating a magnetic field that intermittently opposes the field generated by the permanent magnet. Although this relay purports to be bi-stable, the relay requires consumption of power in the electromagnet to maintain at least one of the output states. Moreover, the power required to generate the opposing field would be significant, thus making the relay less desirable for use in space, portable electronics, and other applications that demand low power consumption.
With regard to optical switches, a further significant challenge relates to alignment of input laser light. Most conventional mirrors used in aligning laser light to an optical fiber or other component generally fall into one of two categories, referred to herein as “flip-up” mirrors or “vertical sliding mirrors”. Before actuation, the “flip up: mirror typically lies flat so that incoming light is not affected by the mirror. After actuation, the mirror typically stands vertically to reflect the incoming laser beam by approximately 90 degrees. At the output of the relay, an optical fiber with a micro lens typically resides in a trench etched on a substrate to collect the laser beam. The mirror may be supported by an actuating arm (or arms) with micro hinges at the bottom to provide a rotation pivot. It can also be supported by flexure springs. Flip-up mirrors are typically actuated by various mechanisms (e.g. a scratch drive, comb drive, impact comb drive, sliding gear with comb drive, simple electrostatic force between mirror and sidewall, magnetic force, or the like).
Unlike the “flip up” mirrors which typically require rotation during actuation, a vertical sliding mirror typically uses a special translation to activate. Typically, the mirror sits vertically on top of a slide. When the mirror is actuated, it slides to a position predetermined by a stopper to intercept the laser beam path and reflects it by 90 degree. Vertical mirrors are typically made by an LIGA(RoentgenLIthographie Galvanik Abformung: X-ray lithography, electrodeposition and molding) process or by deep reactive ion etching (DRIE), followed by a coating with reflective metal. The slope of the mirror may be on the order of about 1/1000 with the LIGA process. The surface smoothness may be on the order of about 5 nm with the DRIE process.
It frequently becomes extremely difficult to align a laser beam reflected by the vertical mirror to the output port in free space when the switch array size becomes large (e.g. on the order of 512×512). Assuming a chip size to be 5 cm, then the switch size needs to be about 5/512, or about 100 micrometers. Because designs typically require alignment accuracy on the order of about 0.012, it becomes extremely difficult to achieve such accuracy with standard microelectronics fabrication techniques. Active mirror fine-tuning can somewhat relieve the problem, but this tuning typically introduces other problems such as complication in fabrication and circuits, slower speed, etc. In addition to the alignment problems, the divergence of the laser beam may also become unacceptable when the array size becomes large (e.g. when the transmission distance exceeds about 1 cm). It is therefore desirable to create an optical switch capable of meeting rigorous design specifications even in large switch fabrics.